They had that ($10/year, one address, fairly small storage limit) but they eliminated it a few years ago. That disappointed me.

The thing about most SaaS companies is a majority of your support calls come from your lowest tier customers. In a service like email where a huge number of problems are a mystery due to other mail servers possibly mishandling email Fastmail have probably added up the numbers and realised that dropping the cheapest plans results in significantly less support costs.